For the production of methacrolein by the vapor phase oxidation of isobutylene various oxidation catalysts have been proposed.
Japanese patent Publn. Nos. 8992/1969 and 25046/1969, for example, disclose the tellurium oxide-molybdenum oxide catalysts. Catalysts containing tellurium, however, are highly toxic and have a short service life due to the dissipation of tellurium so that these catalysts are not suitable for industrial use. Japanese patent Pbuln. No. 32043/1972 and Laid-open Publn. No. 5710/1973 disclose catalysts containing thallium oxides. Thallium oxides tend to be easily reduced in a reducing atmosphere to oxides of lower valence thallium or metallic thallium, both of which are volatile. Furthermore, thallium is poisonous to humans,